Various transdermal devices and systems are known for collecting and monitoring body fluids. For example, in Peck et al, "A Non-Invasive Transepidermal Toxicological Monitoring Device", Pittsburgh Conference and Exposition on Analytical Chemistry and Applied Spectroscopy, Mar. 9, 1982, Meeting Abstracts Book, page 366, a transepidermal device is disclosed including an adhesive plastic chamber containing sodium chloride-impregnated absorbant pads and an activated charcoal impregnated disc for capturing a xenobiotic to prevent back transfer from the collection device into the body. The Peck copending application Ser. No. 660,778 filed Feb. 11, 1985 discloses a dermal substance collection device including a liquid bridge transfer medium for transferring a dermal substance to a binding reservoir material which binds the substance and prevents back transfer loss of the substance from the collection device.
The Phillips U.S. Pat. No. 4,329,999 discloses a dermal patch for collecting sweat from a patient which includes a collecting pad for absorbing sweat. Similarly, the Phillips U.S. Pat. No. 4,595,011 discloses a transdermal dosimeter device including a dermal contact bridge, a fluid collecting component for collecting and storing fluids collected from the skin and a process component for binding or chemically converting the stored substances. The latter Phillips patent suggests that chemical conversion of collected substances to produce an observable color change in the device may be effected.
The Fogt et. al. U.S. Pat. No. 4,444,193 discloses an absorbent patch device for absorbing sweat, which patch device includes a chemical composition capable of reacting with chloride contained in the sweat.
The Pugliese U.S. Pat. No. 4,071,020 discloses an apparatus and methods for performing in-vivo measurements of enzyme activity wherein one or more reactants are placed directly on a predetermined area of the skin surface and are free to migrate into the skin. While the apparatus and methods of Pugliese are not dependent on collection of a substance such as sweat or interstitial fluid, they may be dangerous to the subject if the reactants have toxic effects upon migration into the skin of the subject.
Other devices are also known for measuring substances, particularly gases, in or emanating from the skin. For example, the Clark, Jr. U.S. Pat. Nos. 4,401,122 and 4,458,686 disclose apparatus and methods for measuring substances, particularly gases, which diffuse through the skin or are present underneath the skin in the blood or tissue using polarographic electrodes or enzyme electrodes. The Vesterager et al U.S. Pat. No. 4,274,418 discloses an apparatus for measuring gases, for example oxygen and carbon dioxide, which diffuse from blood vessels and through skin tissue wherein the gas is directed to a measuring chamber in which the partial pressure is measured.
The present inventor has discovered that various substances migrate to the skin surface of a subject by diffusion in the absence of a liquid transport medium such as sweat and has discovered means for producing detectable signals in a transdermal detection system at the skin surface without direct placement of detector chemicals which are capable of migrating into the skin on the skin surface. Known transdermal devices rely on the collection of body fluids such as sweat or gaseous substances emanating from the skin or the binding of substances transferred through a liquid bridge transfer medium, without detection and signalling, or employ direct epidermal application of potentially toxic detector chemicals, and thus are disadvantageous for safely detecting and signaling substances which migrate to the skin surface of a subject by diffusion.